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Possible to supercharge a 2-stroke?

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Posted by: G92Joe

I've heard of 2-strokes being supercharged & turbocharged (snowmobiles, road raacers, more ?) but is the power increase worthwhile? Is'nt the charge lost out the exhaust port? Or is it shoved back in by the returning sound wave from the expansion chamber's convergent cone? I would think the increased crank pressure would also parasitically limit low & mid power, but top-end power would be high - anyone know where I could find more info on this subject? Thanks -


Posted by: Studboy

I have also heard of snowmobiles being turbocharged, but not supercharged. I can't imagine them getting setup correctly because your clutching and jetting would be near impossible to get right. Same thing with Nitrous Oxide on sleds, either you are HORRIBLY rich and overclutched when you are not running it or you burn your sled down and you are underclutched when you are not on the bottle.


Posted by: cujet

Turbocharging works well on two strokes. Keep in mind that the exhaust pressure is increased as well as the intake pressure. I guess a good way to look at it is, that the engine is running in a more dense atmosphere or lower altitude.

Chris


Posted by: jmics19067

Detroit Diesel two strokes are supercharged. The same rootes type blowers you see on hot rods and such. A lot different then piston drawing fresh air under it on the compression stroke and forcing it thru the transfers on the fire stroke as we know it.

At the bottom of the cylinder liner the intake ports are surrounded by a blower box. This box is pressurized air from the supercharger when the piston goes down opening the port the fresh air is pushed thru. Although they do have cam operated exhaust valves just like a four stroke so they have no expansion chamber.


Posted by: techman

I would suggest looking up the specialty companies who do the kits for snowmobiles and doing some head scratching as to why they've done what they do. You might get some pointers directly from them, or maybe even convince them to try their turbocharging skills on a new project. I believe the gains were pretty substantial on sleds, just mid size 500's or 600's. I don't recall anyone doing a big motor sled.


Posted by: WoodsRider

This is what jmics was describing.


Posted by: jmics19067

yep, thats exactly the animal I was trying to describe, thanks.


Posted by: WoodsRider

And this is what two roots blowers mounted on a GP38 locomotive diesel engine look like. Sorry for the poor quality.


Posted by: jmics19067

the guys where I used to work would have WAY too much if I tried squeezing one of them into a forklift


Posted by: Jon K.

Way back when (I hope I have my facts right) some two-strokes were supercharged in an unusual way. They used a large diameter "dummy" piston mounted on the crank. It shared the crankcase with the working piston. The sole purpose of this piston was to increase the primary pumping action.
I never saw one; don't know if it worked.


Posted by: splatt

Quote:
Originally posted by jmics19067
Detroit Diesel two strokes are supercharged. The same rootes type blowers you see on hot rods and such. A lot different then piston drawing fresh air under it on the compression stroke and forcing it thru the transfers on the fire stroke as we know it. 


 

The supercharger on the Detroit Diesels does what the crankcase pressure on the smaller 2-strokes does. They have to have them in order to run at all because none of the intake charge is coming from the crankcase. Adding a turbo will increase the boost thus increasing HP and torque.

 

Steve 


Posted by: Rich Rohrich

Quote:
Originally posted by wfo74
Way back when (I hope I have my facts right) some two-strokes were supercharged in an unusual way. They used a large diameter "dummy" piston mounted on the crank.


It was called a twingle . Eric Gorr used to ride his in the DEAD of winter in Chicago. He still has the frostbite marks from it

Here's some info :
http://allstateguy.tripod.com/allstateguy/id8.html


Posted by: jmics19067

Quote:
Originally posted by splatt


 

The supercharger on the Detroit Diesels does what the crankcase pressure on the smaller 2-strokes does. They have to have them in order to run at all because none of the intake charge is coming from the crankcase. Adding a turbo will increase the boost thus increasing HP and torque.

 

Steve 


true they will not run if the blower drive is wiped out and they dont pump. But the amount of pressure would probably easier to adjust by the size of the blower and/or the ratios of the drive gears than by adding a turbocharger on top of it.


Posted by: Jon K.

Rich; as cool as the twingle is; that is not the engine I was referencing. I did a little digging, but could only come up with some incidental references in this document.

http://www.kawasakitriplesworldwide...kw%20engine.htm

About three paragraphs down. The "dummy" piston did not get a spark; this pistons sole purpose was to push and pull the charge; resulting in a supercharging effect.


Posted by: Rich Rohrich

Quote:
Originally posted by wfo74
The "dummy" piston did not get a spark; this pistons sole purpose was to push and pull the charge; resulting in a supercharging effect.



If memory serves correctly that's how the twingle works too. :thumb:


Posted by: Jon K.

Rich; your reference to http://allstateguy.tripod.com/allstateguy/id8.html is a great example of the twingle. As shown in the animation; both pistons get a spark.

This photo http://www.kawasakitriplesworldwide...gineLayouts.jpg
shows some good examples of the big "dummy" piston (figure #4) that is used to push and pull the charge for the supercharging effect. The big piston does not get a spark; it sole purpose is for supercharging.

Cool stuff. I played around with a similar idea that would pull charge in and out through the main bearing (with seal removed) in a more modern engine, but now believe the concept to be fataly flawed. :whiner:


Posted by: Rich Rohrich

Quote:
Originally posted by wfo74
Rich; your reference to http://allstateguy.tripod.com/allstateguy/id8.html is a great example of the twingle. As shown in the animation; both pistons get a spark.


I have a feeling his animation is incorrect. Eric will likely remember. :thumb:


Posted by: splatt

Quote:
Originally posted by jmics19067


true they will not run if the blower drive is wiped out and they dont pump. But the amount of pressure would probably easier to adjust by the size of the blower and/or the ratios of the drive gears than by adding a turbocharger on top of it.


 

The blowers are specific to the size of the engine. A 6V-71 won't fit a 8V-53 and vice versa. It's been about 12 years since I've worked with them so I don't remember if you can change the drive ratios to increase power.

 

Steve


Posted by: jmics19067

Quote:
Originally posted by splatt


 

The blowers are specific to the size of the engine. A 6V-71 won't fit a 8V-53 and vice versa. It's been about 12 years since I've worked with them so I don't remember if you can change the drive ratios to increase power.

 

Steve


true, I don't know if there is a turbo set up for Detroit diesels. If there is then bolting on an extra existing systems would be relatively easy. I was just merely stating that it is probably easier to modify existing systems that designing and adding an extra system.

One of my brain drizzles was if you were to take a four stroke bottom end and to fit a modified 2 stroke top end to it. Pressurized oiling system on the bottom, use the cam gear on the crank to drive a supercharger where the reed valve would be,no using the crankcase for fuel management, no transfer ports just directly fed into the intake ports over top of the piston. I would think in the right hands this could be a viable project for an engineer with machine shop capabilities to build on weekends to keep from getting bored. The only advantage that would become though that I can see is the possibility of increasing intake volume hopefully increasing power at the risk of heating the intake charge and extra wieght,moving parts, decreasing power.


Posted by: splatt

Quote:
Originally posted by jmics19067


true, I don't know if there is a turbo set up for Detroit diesels. If there is then bolting on an extra existing systems would be relatively easy. I was just merely stating that it is probably easier to modify existing systems that designing and adding an extra system.


 

Turbos were available for the Detroits. A couple of the ones that I worked on had turbos. I would like to see a version of what your describing. I think it would be more durable with a pressure fed oiling system than a conventional 2-stroke but at the same time heavier.

 

Steve


Posted by: ktm 550 mxc monster

Detriot does not offer different drive ratios for the blower simply because it really isn't effective. There are too many systems that also get driven off the blower and speeding up the blower will actually hurt power due to the bottom port design and speeding it up can cause the air to whip more than move with the airbox arrangment in the block. All factory hot rod Detroits use turbos to make the horsepower and a turbo can produce more boost than a supercharger without pumping losses. The only difference between a naturally aspirated (blower) and turbo charged is really hotter injectors, some models varied compression some didn't. Putting a turbo on a Detroit is really a very simple modification, just getting to the blower is usually serious work. We are the Detriot Diesel distributor for DFW and north Texas where I work and rebuild Detroit 4 and 2 strokes that make as much as 3000 horespower and are awesome engines to hear run, they have 2 blowers just to get enough air in it to run and then 4 turbos to make the ponies. Sadly the two strokes are getting harder to get parts for and really fading away mainly due to the fact that they cannot compare with power,longevity, durabilty and most devistating emissions of todays 4 stroke Detriots, but I will never forget the sound or throttle response from a 2 Stroke Detroit, especially the 16V149 pushing in excess of 3000 HP.


Posted by: jmics19067

a picture of what? my brain drizzle is nothing more that just a concept that got cooked up in between my ears. I have no idea if anybody ever thought or experimented with something like that for a motorcycle purpose. I have unscientifically came to the conclusion that space limitations would prevent an adequate sized supercharger to be affixed where the reed cage would be.Or the size of the blower would be so small that you would have to spin it extremely fast causing the intake charge to be too hot,negating any effects of a dense charge. Also the thought of the blower exploding like in drag cars made me leary of the thought of an open port of the cylinder directly hooked to a heated fuel air mixture at the blower right between your legs.

the detroits I used to work with were 4-53n's two strokes that where the 4 cylinder version of the picture that woodsrider posted for me and the series 60 11 litre in trucks.
I didnt realize that detroits with superchargers had turbos as an option since they are on the archaic side because of emmisions and fuel economy. I only saw them on forklifts and for that application they worked great and lasted for quite a long time. The issue of the bottom ring wearing and pumping out the oil was the only thing I saw that never became a serious issue being in a yard close to a shop.Just change the "slugs and jugs" when it used a gallon of oil a day. Aside from setting up the rack I thought they where simply easy to work on with the hardest job for me on those engines was picking up prime when the numbskulls ran them out of fuel.<which also usually meant changing the battery and starter because they would just try and fill it up and crank the snot out of it till something smoked instead of calling us and getting abused while we filled the filters >
The limited Series 60 engines I saw never caught on where I work. The only consistent problems I have seen with them where only teething problems dealing with the computer,shutting off in traffic because of the proposed 3 minute idle rule crap like that. I can't say that they are a bad engine but a lot of the drivers complained about them.ALso they are not available for the cab and chassis that my bosses like<and went back to> so I know very little about them.


Posted by: evenslower

There's a japanese company out there, can't remember the name at the moment but someone may know, that makes commercial lawn equipment with a "supercharged" two stroke. Things like weed eaters, leaf blowers.....smaller applications than what I think has been discussed here so far. If I can find their website I'll post it but they had a some info regarding reduced emissions. A good direction to be thinking with the big bad EPA and all


Posted by: KnobShredder

WFO74 i have a feeling you might be referring to the old supercharged DKW 350 2strokes of the 1940's. i think they actually had 3 pistons - an extra piston for supercharging and one for port timing. these bikes had straight tuned exhausts, and consumed vast quantities of fuel - so much so that they needed enormous fuel tanks. i have a feeling these bikes were the all-time "unburned hydrocarbon kings" lol


Posted by: KnobShredder

http://www.kawasakitriplesworldwide.com/triples/gallery/dkw/DKWEngineLayouts.jpg


Posted by: jaction125

I think the only Detroits w/turbo and blower were called "Silver" 92 series, we still see some of them in old refuse trucks and busses.


Posted by: Jon K.

Quote:
Originally posted by KnobShredder
http://www.kawasakitriplesworldwide.com/triples/gallery/dkw/DKWEngineLayouts.jpg


Knob; yes, in fact that is the same link I posted. That was the only reference that I found.
Here is one of the actual bikes; note the dummy cylinder poking out the bottom.
Edit; hmmm . . . give me a minute on that photo.


Posted by: Jon K.

Ahhh . . . There it is.



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